In the sale and supplying of liquefied petroleum gases, (LP-gases) such as propane or others to customers and in particular, residential customers, it has been a common practice for the supplier to provide a gas supply tank to the customer installed on the customer's premises at no up-front cost to the customer. The supplier will then gradually recover the cost of the tank by including it in the amount the customer pays for the gas delivered by the supplier. This arrangement is based on the concept that the tank is owned by the supplier that installs the tank and only the owner of the tank is permitted to fill the tank.
Some suppliers have adopted the practice of filling tanks owned by other suppliers and thereby obtaining the free use of another supplier's tank. This creates a situation where the tank owner is not only, being deprived of a way of recovering the cost of the tank which he has provided, but he may incur legal liability if an unauthorized supplier negligently fills the tank and causes an accident or explosion since he may be wrongfully blamed for the accident. To prevent this unauthorized use by suppliers who do not own the tanks, it is necessary to customize the fill fitting of the tank so that it will not be compatible with the outlet end coupling of a fill hose of suppliers other than the tank owner.
An example of one type of customized or coded coupling is shown in U.S. Pat. No. 4,665,960 (Brzezicki et al.) which uses nuts having a number of different configurations of projections thereon with each configuration matching a certain groove configuration on a mating member. The coupling cannot be connected together unless the matching combination of projections and groove configurations is used. This coupling is used to assure that coupling parts intended for one particular type of fluid cannot be mated with coupling parts intended for other fluids. This type of coupling would not, however be compatible for use with existing fill fittings for tanks such as those used for LP-gases such as propane and would be more complex than necessary where a simple customizing adapter is needed to convert a standard fill fitting to a custom fitting.
One of the unique problems encountered in customizing fill fittings for tanks containing LP-gases is that once the tank has been filled and substantially emptied there is still some gas under pressure within the tank making it unsafe or impractical to remove and replace the fill fitting. It is therefore necessary to be able to customize the fitting by covering the standard male threads of the tank fitting with an adapter which provides non-standard male threads which a standard hose coupling cannot be connected to. It is also important to provide a tamper-proof adapter which cannot be removed from the fill fitting without damaging the standard male threads on the fitting so that they are no longer usable by an unauthorized supplier.